1. Field of the Invention
The present invention relates to an image signal generating apparatus that causes a plurality of display units each having their own identification data to display individual images, an image signal generating method that is implemented by the aforementioned image signal generating apparatus, a program for causing a computer system to implement the aforementioned image signal generating method, and a computer-readable information storage medium that contains the aforementioned program.
2. Description of the Related Art
The Japanese Patent Kokai (Laid-Open) Publication No. 2000-352962 published on Dec. 19, 2000 discloses a system wherein a single image signal generating apparatus (e.g., a personal computer) causes a plurality of display units (e.g., CRT monitors or liquid crystal monitors) to display individual images. FIG. 12 schematically shows three display screens (i.e., a coordinate plane including display regions of first, second and third display units 11, 12 and 13 arranged side by side), on which images corresponding to an image signal output from the image signal generating apparatus are displayed. Further, FIG. 13 is a timing chart showing transmission timing of an image signal output from the image signal generating apparatus.
In FIG. 12, reference numerals 31, 32 and 33 denote indexes that are displayed on the display screens according to an index signal, and reference numerals 41, 42 and 43 denote windows that are displayed on the display screens under control of an application software. Further, a reference numeral 51 denotes a pointer such as a mouse pointer. Furthermore, reference numerals 71, 72 and 73 denote the display screens (or display regions) of the first, second and third display units 11, 12 and 13. The images displayed on the display screens 71, 72 and 73 corresponds to a first page image signal P1, second page image signal P2 and third page image signal P3 in FIG. 13 respectively.
Identification data (e.g., ID Numbers) are previously set for the respective display units 11, 12 and 13 to be used in this system. The image signal generating apparatus used in this system includes a memory device such as a semiconductor memory and reserves a memory space for temporally holding an image signal in the memory device. A size of the memory space corresponds to the number of pages (three in this example), which is equal to the number of the display units (three in this example) shown in FIG. 12. The image signal generating apparatus outputs the first page, second page and third page image signals P1, P2 and P3 corresponding to the respective images of the display screens 71, 72 and 73 on a time division basis as shown in FIG. 12. An index signal is added to the first page, second page and third page image signals P1, P2 and P3 for each frame. The first page, second page and third page image signals P1, P2 or P3 are sequentially supplied to all the display units 11, 12 and 13 connected to the image signal generating apparatus as shown in FIG. 12.
Each of the display units 11, 12 and 13 judges whether or not the index signal added to the received image signal P1, P2 or P3 for each frame coincides with its own identification data. The display unit 11, 12 or 13 that has an identification data coinciding with the index signal, displays an image based on the image signal P1, P2 or P3 for each frame having the index signal (i.e., the display unit rewrites the contents of its image memory). On the other hand, the display unit 11, 12 or 13 that has an identification data not coinciding with the index signal, ignores the received image signal P1, P2 or P3 for each frame having the index signal and does not change the displaying image (i.e., the display unit does not change the contents of its image memory).
In this system, only by connecting the single image signal generating apparatus and the plurality of display units by means of a connection cable or cables, a single image can be displayed on a broad area made up of the display regions of the plurality of display units, or a plurality of windows based on an application software can be displayed on the respective display regions of the plurality of display units.
As described above, in the aforementioned conventional system, the image signal generating apparatus reserves a memory space, a size of which corresponds to the number of pages (i.e., the number of display units), and switchingly outputs the first page, second page and third page image signals P1, P2 and P3 for each frame on a time division basis. Therefore, a large amount of the memory space must be reserved in the memory device of the image signal generating apparatus, thus undesirably increasing the price of the system.